Enzymes as Biocatalysts for Lipid-based Bioproducts Processing - Food and Industrial Bioproducts and Bioprocessing - page 342

limited miscibility, which lead to lower mass transfer, reaction rate and product yield.
In addition, the presence of insoluble alcohol also leads to lipase inactivation. As mentioned
earlier, the problem of substrate immiscibility can be overcome by using organic solvent,
emulsifier, or FAAE as co-solvent.
Another important bottleneck in enzymatic processing of FAAE is adsorption of glycerol
onto the biocatalysts beads. Glycerol adsorption inactivates enzymes, particularly in con-
tinuous and repeated batch processes which employed same batch of enzyme in the repeated
production cycles (Antczak et al ., 2009 ; Fjerbæk et al ., 2009 ). The problem of glycerol
adsorption can be solved by using membrane reactors, filters or separators (Belafi-Bako
et al ., 2002 ; Fjerbæk et al ., 2009), suitable solvents as washing or flushing systems for
glycerol removal and addition of porous hydrophilic particles, such as micro-porous sieves
and silica gel, to the enzyme bed for glycerol adsorption (Dossat et al ., 1999 ).
In conclusion, robust and economical biocatalysts with improved activities, the use
of inedible oils and waste oil as potential feedstocks and optimized reaction conditions for
different substrates and biocatalyst pairs will determine the possibility of industrially
sustainable enzymatic FAAE production.
14.5 CONCLUSIONS AND FUTURE TRENDS
Production cost and efficiency are the key concerns in industrial applications of biocatalysts.
The need for production cost reduction is far more critical than ever. Therefore, concept
development is no longer the key issue for enzymatic processing. Rather, optimization of
the enzymes for efficient conversions and processes is the goal for broader use of enzyme
technology in industrial applications. Although enzymes still comprise a substantial part of
the operating costs, their share is relatively small considering the large total production cost
of some of the biocatalysis products. Therefore, improvements in process and system design
and operation are the key to cost reduction.
Figure 14.6 shows a typical flowchart of engineering enzymes as catalysts for efficient
bioprocessing. Major challenges in industrial applications of biocatalysis are the identification
and selection of suitable enzymes for the formation of desirable reaction products; this can
be done using high-throughput screening technologies, which involve collecting genes from
the environment and expressing them in recombinant organisms (Arnold, 2001; Van Beilen
and Li 2002; Arnold, 2001). These methods allow faster access to useful catalysts from
organisms that cannot be cultured. Once the enzymes of interest are identified or selected,
they have to be separated and purified, as most enzymes exist with many isomers or
other proteins.
In nature, enzymes play an important role in the survival and reproduction of their source
organism. Therefore, many enzymes in their natural form are not suitable for application
directly as biocatalysts in bioprocessing. For example, most enzymes are active at relatively
mild conditions, thus may not be viable under the harsher conditions encountered in most
industrial production systems. Various methods have been used to improve the properties
of enzymes, including selectivity, activity and thermostability, in order to enable them to
function as efficient industrial biocatalysts. Enzyme engineering, which encompasses
rational design and directed evolution, is an efficient method to improve enzyme properties.
Rational design seeks for beneficial mutations or protein sequences by applying empirically
derived rules or theoretical models. Meanwhile, directed evolution uses a combinatorial
approach to create libraries of enzymes from which enhanced variants can be identified